Residence time effects during capillary flow of a rigid PVC formulation

A typical rigid PVC formulation was rheologically characterized using capillary and parallel plate rheometers within regular processing temperatures and deformations. At 190°C and in an intermediate range of shear rates (10 to 100 l/s) the stress response was a function of the flowing time in the capillary. This behavior was not observed at other temperatures (170 and 210°C). Small amplitude oscillary shear experiments for the same compound but with various thermomechanical histories showed a different behavior as compared to the results of the capillary flow. The specific results of the capillary experiments are consistent with the hypothesis of particulate flow of PVC and also point out the influence of the stabilizers and lubricants in the flow behavior of the compound. The time dependent effect is analyzed in terms of the coupling of thermal and mechanical stresses with the unmelted particles present in the flow field.     

Viscous dissipation and apparent wall slip in capillary rheometry of ice cream

We have analysed sets of capillary rheometry data (0.3 s^?1 ≤ γ_app ≤ 360 s^?1) for a commercial ice cream as it flowed from a freezer on an industrial flow line. Pressure drop measurements were used and particular attention was paid to viscous dissipation effects. A semi-analytical model presented by Bird in 1955 indicated that over one third of the data points were subject to local wall heating, which was consistent with available temperature measurements. The filtered data were used to construct a viscosity function which, when implemented in a detailed CFD simulation of the flow, predicted the observed flow curve behaviour. The results demonstrate that viscous dissipation can be significant in ice cream and that interpretation of this behaviour in terms of wall slip is erroneous.     

Viscous dissipation in packed beds

Factors affecting the magnitude of viscous dissipation in packed beds under conditions used in high pressure liquid chromatography are investigated. The free surface model is employed to characterize packed beds, to evaluate the flow field and to derive the appropriate similitude criterion for the effect of viscous dissipation. Equations for the calculation of radial temperature profiles due to internal heat generation in beds with axially uniform and non-uniform wall temperatures are given and the results are illustrated for typical cases. The evaluation of the temperature profiles in beds with non-uniform wall temperature is based on experimentally measured wall temperatures.     

Anomalous behavior of unplasticized PVC compounds in capillary flow

Capillary rheometry was performed over a temperature range of 170°–200°C and a shear-rate range of 3–3000 sec^?1 on an unplasticized poly(vinyl chloride) compound. The data were corrected for the effect of pressure on viscosity, for pressure loss in the barrel and at the capillary entrance, and for the non-Newtonian velocity profile. The pressure coefficient of viscosity was found to be in the same order of magnitude as those previously found with linear polyethylene and butadieneacrylonitrile copolymers. The pressure–shear-rate superposition of the flow curves is valid at least approximately, although the temperature–shear-rate superposition is inapplicable. The shape of flow curves at 180°, 190°, and 200°C are concave downward when they are expressed as log-shear-stress-log-shear-rate. Similar plots at 170° and 175°C, however, are very different; shear stress is independent of shear rate at low shear rates, increases somewhat and becomes independent of shear rate again at high shear rates. There is no detectable temperature dependence of flow behavior at 170° and 175°C. Irregularly shaped extrudates were obtained at higher shear rates. At constant shear rate the irregularity increased with the length of the capillary. The effect of thermal-mechanical history on the particulate and crystalline structure is discussed with possible influence on the reproducibility of the rheological data.     

Viscous dissipation in plastic pipe extrusion

We study the temperature distribution of a power‐law fluid in a pressure‐driven axial flow between eccentric cylinders in bipolar cylindrical coordinates. We begin our analysis by writing the equation of energy in bipolar cylindrical coordinates. We then obtain a dimensionless algebraic analytic solution for temperature profiles under a steady, laminar, incompressible, and fully developed flow for an adiabatic core and an isothermal outer cylinder (Eq. 59 ). We find that the dimensionless temperature profile depends upon the radius ratio of the inner to outer cylinders, the eccentricity, the angular position, and the power‐law exponent n. The temperature is a strong function of the gap between the cylinders. Finally, dimensionless maximum temperatures are plotted to help pipe manufacturing engineers prevent excessive heating during production. POLYM. ENG. SCI., 53:2205–2218, 2013. © 2013 Society of Plastics Engineers     

Fusion mechanism in rigid PVC

A classic approach for studying network effects in carbon‐black‐containing rubber was applied to PVC with stabilizer. This approach involves measuring the shear modulus with increasing strain. In carbon‐black‐containing rubber, the modulus drops dramatically at a critical strain level. This is known as the Payne effect and is associated with the breakup of the carbon black network. Rigid PVC that is fused to different levels in a bowl mixer shows exactly the same behavior, and the drop point correlates very well with the fusion peak in the mixing bowl. The relationship between network effects and fusion in PVC is discussed.     

Viscosity effects in rigid PVC

The viscosity of PVC is better understood if the material is treated as a fluid which contains filler. Anomalous effects such as die swell increasing with increasing melt temperature and melting history causing changes to the viscosity can be explained if the PVC primary particles are viewed as filler which disappears during melting. The fusion torque peak is well‐described by this approach. The compaction minimum is a free‐flowing powder which changes to a filler‐containing viscous liquid. If another viscous liquid is added to a PVC compound, then the fusion peak will be at a lower torque, because the effective level of filler is reduced. This reduction helps to explain the fusion curve of PVC compounds that contain chlorinated polyethylene (CPE) impact modifier.     

微尺度通道中聚合物熔体的黏性耗散效应

以双料筒毛细管流变仪和自行研制的黏性耗散测量装置为实验平台,通过对聚甲醛(POM)和聚苯乙烯(PS)两种聚合物熔体在不同剪切速率下,流经长径比相同的直径/当量直径分别为350 μm和500 μm的圆形及矩形截面微通道出口熔体温升的测量,研究了微尺度通道中聚合物熔体流动时的黏性耗散效应及其对熔体流变行为的影响。结果表明,两种截面微通道中的熔体黏性耗散效应均随剪切速率和微道直径/当量直径的增大而明显增强,其中矩形截面微通道中熔体的黏性耗散作用尤为强烈;且在相同实验条件下,结晶性的POM熔体因黏性耗散效应引起的微通道出口熔体温升值,高于非晶性的PS熔体。     

Blends of rigid PVC and polystyrene

Several compatibilizing agents were investigated to stabilize blends of rigid poly(vinyl chloride) and polystyrene. Copolymers of alpha-methyl-sytrene and methacrylonitrile were made by emulsion polymerization. These products, with alpha-methylstyrene contents varying between 50 and 75 weight percent, could be blended with the two primary polymers to produce alloys with good processability and strength. Styrene-acrylonitrile copolymers with 70 and 75 percent styrene content were also found to provide useful polyblends. All mixtures were opaque. Compositions containing at least 30 weight percent PVC were self-extingushing. Polystyrene-poly(vinyl chloride) mixtures with as little as 7.5 weight percent styrene-acrylonitrile copolymer appear to have adequate mechanical strength and processability for commercial applications. Some end-uses for variations of these polyblends are suggested.     

ABS and CPE modifiers in rigid PVC

A comparison of acrylonitrile butadiene styrene (ABS) and chlorinated polyethylene (CPE) as PVC modifiers showed ABS to improve processability at low concentrations. CPE is more effective at high levels. Almost all the modifiers improved impact strength dramatically at 10 parts per hundred of resin. CPE containing 36 percent chlorine was the most effective, but reduced PVC modulus and heat-deflection temperature more than ABS.     

Shrinkage in rigid PVC profile extrusions

Shrinkage in PVC profile extrusions may have an effect on the end use performance (dimensional stability, mechanical properties) of the building products such as house siding and windows when they are heated by the sun. This paper examines the heat shrinkage tests being used in the industry, and most importantly, describes effects of the extrusion conditions such as melt temperature, shear rate, percent drawdown, and other variables on shrinkage in PVC profiles.     

Lubricant behavior in rigid PVC rheology

Capillary rheometry was carried out on lubricated suspension PVC resin at a temperature of 180°C and a shear rate range of 1.5 to 350 sec⁻¹ to specify lubrication efficiency. Correction and discussion for the effects of pressure, non-Newtonian behavior and viscous heating were done. An indication that the lubricant is localized in the resin free volume appears from pressure coefficient variation. Corrected capillary rheometry showed to be sensitive for low lubricant concentrations (0.3 to 2 Phr) similar to those used in commercial compounds.     

Processing window in impact-modified rigid PVC

A method is described for quickly evaluating the processing window of impact-modified rigid PVC formulations. This involves mixing the compound in a bowl mixer at various temperatures and to various levels of total work input. The impact properties are measured and plotted as a contour map versus melt temperature and work input. The melt temperature is the dominant factor in controlling the impact processing window. The total work input is a secondary effect, which mainly influences the system through shear heating effects on the melt temperature. This method was used to evaluate formulations with different impact modifiers and lubricant and filler levels. Impact modifier type, polyethylene wax, and filler concentrations are the dominant factors. The mechanisms involved are discussed.     

Adsorption behavior and shear degradation of ultrahigh-molecular-weight hydrolyzed polyacrylamide in a capillary flow

Ultrahigh-molecular-weight partially hydrolyzed polyacrylamides (HPAMs) are commonly used in polymer flooding to enhance oil recovery. However, the viscosity of the HPAM solution is susceptible to shear action. Viscosity change affects sweep range and displacement efficiency of the displacement fluid. Here, a macromolecular adsorption model in microcapillary is proposed to reveal the shear variation mechanism at low flow rates. The rheological behaviors of HPAMs with three different molecular weights are investigated using a stainless steel capillary. The shear rate distributions near contraction and within capillary are compared by numerical calculation using the laminar flow model. Experimental and numerical results show that the polymer solution was mechanically degraded at low flow rates, which is in agreement with the results predicted by the adsorption theory model. A new calculation method for the thickness of polymer adsorption layer at lower flow rates is proposed based on the adsorption model proposed in this study. It is found that the viscosity and adsorption of HPAM were changed with flow rate, and their changes are closely related to the displacement efficiency in the micropores of reservoirs. This study provides new perspectives for the selection of polymer injection flow rates and the water shutoff in reservoirs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48270.     

PVC-U的润滑平衡

提出了加工PVC-U时润滑平衡的确切定义及现实意义,以扭矩流变曲线上的塑化时间、塑化扭矩值作为评价润滑平衡的定量标准,指出了润滑平衡的研究方法及实验程序。     

Mechanical degradation of dilute solutions of high polymers in capillary tube flow

Experimental results on mechanical degradation in capillary tubes of polyisobutylene polymers in dilute solution are described. In laminar flow, degradation is independent of tube length, indicating that entrance effects are dominant. This shows that capillary experiments do not yield explicit information on the effect of shear stress on mechanical degradation. In turbulent flow, large entrance effects are also observed, but some degradation does take place in the fully developed flow region.     

Inert-gas extrusion of rigid PVC foam

A novel approach to the extrusion of high-density, rigid PVC foam uses commercial RPVC compounds with inert-gas physical blowing agents (carbon dioxide and argon). The process was developed on a segmented single-screw extruder with L/D of 40. On-line monitoring of process variables was also carried out. This technique provides an alternative to conventional processing methods using chemical blowing agents.     

硬质聚氯乙烯管道的技术进步

介绍了PVC-U管道行业的整体情况、PVC树脂及加工助剂的应用情况、建筑用PVC排水管道和压力管道的技术进步,指出了PVC-U管道存在的主要问题和差距,并给出了发展建议。     

Changes in properties of rigid PVC during weathering

Changes in properties of PVC compounds upon weathering are categorized as due to physical aging or due to chemical change. PVC's tensile strength, flexural strength, tensile modulus, and flexural modulus generally rise slightly with weathering. DSC data on weathered samples show an annealing effect identical to physical aging. The impact strength of weathered PVC is substantially lower than expected from physical aging. Molecular weight of PVC on the weathered surface is lowered upon weathering. Thus the loss of impact strength of PVC upon weathering is mainly due to chemical change.